Along an assembly line, various types of articles, such as for example, diapers and other absorbent articles, may be assembled by adding components to and otherwise modifying an advancing, continuous web of material. For example, in some processes, advancing webs of material are combined with other advancing webs of material. In other examples, individual components created from advancing webs of material are combined with advancing webs of material, which in turn, are then combined with other advancing webs of material. Webs of material and component parts used to manufacture diapers may include: backsheets, topsheet, absorbent cores, front and/or back ears, fastener components, and various types of elastic webs and components such as leg elastics, barrier leg cuff elastics, and waist elastics. Once the desired component parts are assembled, the advancing web(s) and component parts are subjected to a final knife cut to separate the web(s) into discrete diapers or other absorbent articles. The discrete diapers or absorbent articles may also then be folded and packaged.
Various methods and apparatuses may be used for attaching different components to the advancing web. Some production operations are configured to advance substrates in a machine direction at a constant speed. However, when advancing webs have components added thereto or are otherwise subjected to processing operations during production, it may be necessary to slow or stop the advancing web. For example, it may be necessary to slow or stop an advancing web passing through a processing station configured to perform such operations as, for example, gluing, welding, and adding discrete components. In an attempt to avoid having to vary the speed of the entire length of a substrate passing through an assembly line, some devices can be used to vary the speed of a portion of the substrate without affecting the speed of the entire substrate. However, such devices may only be configured to slow or stop the portion of the advancing web passing through a processing station for an instant or a very short duration of time. In turn, the processing stations may not be able to complete their respective functions during the relatively short time period while the web is slowed or stopped. In addition, some speed varying devices are configured to engage both sides an advancing web, which may have a negative impact on other process steps.